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Date: Sat, 14 May 2005 18:28:00 -0000
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From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/21541] [4.1 Regression] gcc.c-torture/execute/20031215-1.c compilation fails
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X-SW-Source: 2005-05/txt/msg01921.txt.bz2
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------- Additional Comments From rguenth at gcc dot gnu dot org  2005-05-14 18:28 -------
gimplify_expr calls fold_indirect_ref on *(char *)&ao.ch which happily folds
away the cast.  Disabling fold_indirect_ref leaves the stripping to
STRIP_USELESS_TYPE_CONVERSION, so we end up with

  const char * D.1237;

  D.1237 = &ao.ch;
  *D.1237 = 1;

resulting from gimplify_expr (
 <nop_expr 0x401462c0
    type <pointer_type 0x40156bd0
        type <integer_type 0x401493cc char public QI
            size <integer_cst 0x40141210 constant invariant 8>
            unit size <integer_cst 0x40141228 constant invariant 1>
            align 8 symtab 0 alias set -1 precision 8 min <integer_cst
0x40141270 -128> max <integer_cst 0x401412d0 127>
            pointer_to_this <pointer_type 0x40156bd0>>
        unsigned SI
        size <integer_cst 0x40141408 constant invariant 32>
        unit size <integer_cst 0x40141198 constant invariant 4>
        align 32 symtab 0 alias set -1>
    readonly constant invariant
    arg 0 <addr_expr 0x401462a0
        type <pointer_type 0x4015821c type <integer_type 0x401581b0 char>
            unsigned SI size <integer_cst 0x40141408 32> unit size <integer_cst
0x40141198 4>
            align 32 symtab 0 alias set -1
            pointer_to_this <pointer_type 0x4015857c>>
        readonly constant invariant
        arg 0 <component_ref 0x4014e078 type <integer_type 0x401493cc char>
            readonly arg 0 <var_decl 0x401be000 ao> arg 1 <field_decl 0x401b7dec
ch>>>>
)

and tree_ssa_useless_type_conversion_1 tells us that the conversion from

 <pointer_type 0x4015821c
    type <integer_type 0x401581b0 char readonly QI
        size <integer_cst 0x40141210 constant invariant 8>
        unit size <integer_cst 0x40141228 constant invariant 1>
        align 8 symtab 0 alias set -1 precision 8 min <integer_cst 0x40141270
-128> max <integer_cst 0x401412d0 127>
        pointer_to_this <pointer_type 0x4015821c>>
    unsigned SI
    size <integer_cst 0x40141408 type <integer_type 0x40149288 bit_size_type>
constant invariant 32>
    unit size <integer_cst 0x40141198 type <integer_type 0x4014921c unsigned
int> constant invariant 4>
    align 32 symtab 0 alias set -1
    pointer_to_this <pointer_type 0x4015857c>>

to

 <pointer_type 0x40156bd0
    type <integer_type 0x401493cc char public QI
        size <integer_cst 0x40141210 constant invariant 8>
        unit size <integer_cst 0x40141228 constant invariant 1>
        align 8 symtab 0 alias set -1 precision 8 min <integer_cst 0x40141270
-128> max <integer_cst 0x401412d0 127>
        pointer_to_this <pointer_type 0x40156bd0>>
    unsigned SI
    size <integer_cst 0x40141408 type <integer_type 0x40149288 bit_size_type>
constant invariant 32>
    unit size <integer_cst 0x40141198 type <integer_type 0x4014921c unsigned
int> constant invariant 4>
    align 32 symtab 0 alias set -1>

is useless because c_types_compatible_p in turn thinks "char" and "const char"
are compatible because they share the same TYPE_MAIN_VARIANT "char".

So we finally strip the NOP_EXPR doing the cast to char* from const char*.

If we disable that part of tree_ssa_useless_type_conversion_1, we don't ICE
any longer, but alias1 still does not insert V_MAY_DEFs here and dce1 finally
deletes the store.  Which may be a valid optimization; .t17.alias1:

test1 ()
{
  char * D.1237;

<bb 0>:
  D.1237_1 = (char *) &ao.ch;
  #   VUSE <SFT.0_2>;
  *D.1237_1 = 1;
  return;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21541